1. Field of the Invention
The present invention relates to an optical information recording medium, and in particular, to an optical information recording medium which is suitably used as a recording medium for music.
2. Description of the Related Art
Optical information recording media, in which information is recorded and the recorded information is played-back by laser light or the like, are called optical discs, and among these, compact discs (CDs) for music playback are the most widely known. Further, writable optical information recording media (CD-R) are also used. In these optical information recording media, a digital recording/playback method is used in which recording is carried out by analog signals being converted into digital signals and the digital signals being recorded, and playback is carried out by the digital signals being converted into analog signals and the analog signals being played back. In this digital recording/playback method, even if errors occur during the time from recording to playback, if the playback device can read encoded pulse strings, the errors can be corrected such that the original analog signals can be reproduced. Thus, conventionally, effects that the structure of the optical information recording medium itself has on the recording/playback characteristic have been thought to be small.
Although few in number, there have been inventions which focus on the effects that the structure of an optical information recording medium has on the recording/playback characteristic. For example, Japanese Patent Application Laid-Open (JP-A) No. 2-214078 discloses an invention which improves the playback sound quality of a compact disc. In this invention of JP-A-2-214078, one surface of an optical disc is covered by layer which is formed from a soft, flexible material such as rubber and absorbs and dampens vibrations, and the natural frequency of the disc is absorbed by the soft, flexible member, so as to improve the quality of the playback sound. However, there is the problem with this optical disc of JP-A-2-214078 in that vibration of a frequency which differs from the natural frequency of the optical disc is generated, such that an improvement in sound quality is not always obtained. Further, since a material such as rubber or the like is layered on the disc surface, problems arise with the handling of discs, such as plural discs stick to one another, it is difficult to write with a pen or pencil on the surface of the disc, and the like.
In recent years, as the popularity of CD-Rs has increased, copy-protected CD-Rs exclusively for music have been developed, and further improvement of the recording/playback characteristic (especially sound quality) has been required.
An object of the present invention is to provide an optical information recording medium having improved sound quality.
In order to achieve the above object, the present invention provides an optical information recording medium comprising: either a disk-shaped transparent substrate on which is provided a recording portion formed from a light absorbing layer in which information can be recorded by laser light, or a disk-shaped transparent substrate provided with a recording portion in which information which can be played-back by laser light is recorded; a light reflecting layer provided on the recording portion; and a stabilization layer formed from a material having a density of 1.4 to 4.2 g/cm3 and provided on the light reflecting layer, such that a center of gravity of the optical information recording medium is included within a range of 15% of a radius of the optical information recording medium from a center of the optical information recording medium.
Since this optical information recording medium comprises the stabilization layer formed of a material having a density of 1.4 to 4.2 g/cm3, which is a relatively heavy material compared to other materials of the medium, sounds whose balance is good from the intermediate frequency to the low frequency in the audible range and which are stable and pleasant can be obtained. Further, the stabilization layer is provided such that the center of gravity of the optical information recording medium is within a range of 15% of the radius of the optical information recording medium from the center of the optical information recording medium in order to avoid excessive eccentricity of the optical information recording medium. Although the reason why the optical information recording medium results in improved sound quality is unclear, it is thought that the stabilization layer presses the optical information recording layer in a perpendicular direction such that the optical information recording medium is stable, and as a result, vibrations during rotation are suppressed such that sound quality is improved.